change the type property

modules/overlay/custom/CustomBillboard.js

@@ -17,7 +17,6 @@ class CustomBillboard extends Overlay {
     this._position = Parse.parsePosition(position)
     this._icon = icon
     this._size = [32, 32]
-    this.type = Overlay.getOverlayType('custom_billboard')
     this._state = State.INITIALIZED
   }